The present invention relates generally to voltage source inverters, such as are used in motor drive applications. More particularly, the present invention relates to a method and apparatus for determining an effective DC bus voltage present within a voltage source inverter.
Voltage source inverters (VSIs) are commonly used in motor drives and other applications to control the magnitude and frequencies of voltages in these systems. It is generally desirable to be able to obtain an accurate measure of the effective DC bus voltage present within a VSI, as such a measure is useful for monitoring, control, and to obtain optimal VSI performance in different operating conditions. However, a wide variety of VSI's are known, many of which have designs or bridge topologies which make it difficult to directly measure the effective DC bus voltage. For example, multi-level VSI bridges are known which contain multiple internal DC buses. Conventionally, such bridges require multiple voltage sensors for direct measurements of the bus voltages. This solution is impractical because it typically requires high cost sensors in order to achieve a relatively high level of voltage isolation, and because the use of multiple sensors places a significant I/O burden on the control circuitry associated with the VSI.
In view of the limitations of the techniques described above, it would be desirable to be able to determine the effective DC bus voltage present within a VSI without the need for direct bus voltage measurement. It would further be desirable to be able to determine the effective DC bus voltage of the VSI regardless of the topology of the VSI bridge. It would also be desirable to accurately determine effective DC bus voltage in both transient and steady state conditions.